Conventional leather is formed by tanning animal hides. The tanning process treats an animal hide with a variety of substances to improve and maintain leather's desirable physical characteristics for use in clothing, upholstery, luggage and like applications. The most desirable physical characteristics of tanned leather include appearance, feel, resilience to stretching, longevity, treatability with a variety of surface conditioning finishes and natural drape.
Leather's desirable characteristics are attributed in part to its being a fibrous, semi-porous material made up of an entangled, open matrix of resistant collagen fibers. Collagen fibers make up majority of leather's composition. Collagen fibers are made up of constituent collagen fibril bundles made up in turn by smaller elongated strands of collagen protein known as collagen fibrils.
The tanning process is directed primarily toward collagen fibers to fix chemically reactive sites between adjacent collagen molecules. This links the matrix of resistant collagen fiber bundles, leaving tanned leather pliable, and occupies reactive sites that otherwise would allow leather to degrade and rot. The tanning process likewise removes other compounds from the hide that may be susceptible to degradation and/or perform other functions in the hide that may be replaced with other materials.
Obtaining natural leather is problematic due to supply hide having varying qualities, tanning process costs, varying hide costs over time among other challenges.
The leather harvesting, tanning and preparation process produces waste leather byproducts in leather scraps and shavings. If not otherwise used, the waste leather is disposed of by landfill or incineration, creating a negative environmental impact.
Artificial leather products containing waste leather, such as bonded leather, attempt to emulate natural leather. Bonded leather is synthetic leather formed by embedding shredded leather particles into various binding materials. The shredded leather and binding material substance may be applied onto a fabric backing carrier. Bonded leather type synthetic leathers lack the above-noted desirable characteristics of natural leather. This is due to synthetic leathers lacking the continuous matrix of resistant collagen fiber bundles found in natural leather.
The failure of known artificial and synthetic leathers that contain shredded leather particles is that the individual particles do not physically interact to reproduce or emulate the characteristics of a continuous piece of natural leather having an entangled matrix of resistant collagen fibers. Most notably, artificial and synthetic leathers suffer as lacking desirable tensile strength qualities, other strength qualities and esthetic attributes.
In tests applied by a conventional tensometer, artificial and synthetic leather samples of 0.010 to 0.080 inch thickness were subjected to pulling stresses under tension to failure. Measurement of maximum applied force before failure was recorded and calculated as maximum tensile strength PSI measurements ranging generally from about 790 pounds per square inch (PSI) to about 1750 PSI. Likewise, given the inherently variable makeup of organic animal hides and tanning treatments, the tensile strength qualities of tanned natural leather can vary widely. The tensile strength of representative natural tanned leathers were found to vary from about 2000 to 3200 PSI depending on leather quality, mechanical treatments and coatings applied to the leather.
Processes for forming other types of formed leather substrates containing shredded and fibrillated collagen leather fibers derived from waste derived leather are known. A challenge with these processes is the inability to achieve high levels of fibril dispersion so that subsequently formed leather substrates have the potential for fibril to fibril entanglement. Other challenges are that formed interim wet lap products are difficult to dewater and represent a limit to the degree of fibril dispersion which can be achieved in a final leather substrate product. Wet lap may refer to a sheet comprising the dispersion, where particles or fibers are suspended in a fluid (i.e., a slurry) and the wet lap may be pressed or otherwise manipulated to eliminate at least a portion of the fluid.
The interim wet lap products of these processes also tend to have low wet lap strengths. This presents possessing challenges with manipulating interim wet lap products in large scale production processes using known paper-type processing machines. During transition of the interim wet lap from wire mesh sections of paper-type processing machines, the wet lap tends to break reducing process efficiency and making it very difficult or impossible to produce the end product on a large scale.
Thus, there is a need for an improved formed leather product that is created from available waste leather by-products that reproduces desirable physical characteristics of natural leather. The improved leather product should reproduce the collagen fiber matrix that is found in natural leather, have predicable physical characteristics including high tensile strength, desired elastic properties for a range of end applications and treatability by conventional leather conditioning substances. The process of creating the improved leather product should allow improved de-watering of interim wet lap products and have good wet lap strength to facilitate physically manipulating interim wet lap products.